Diffusion-limited deposition of dipolar particles

Deposits of dipolar particles are investigated by means of extensive Monte Carlo simulations. We found that the effect of the interactions is described by an initial, non-universal, scaling regime characterized by orientationally ordered deposits. In the dipolar regime, the order and geometry of the clusters depend on the strength of the interactions and the magnetic properties are tunable by controlling the growth conditions. At later stages, the growth is dominated by thermal effects and the diffusion-limited universal regime obtains, at finite temperatures. At low temperatures the crossover size increases exponentially as T decreases and at T=0 only the dipolar regime is observed.Comment: 5 pages, 4 figure

Depinning and wetting in nonequilibrium systems

We present an extension of equilibrium wetting to nonequilibrium situations particularly suited to systems with anisotropic interactions. Both critical and complete wetting transitions were found and characterized. We have identified a region in the space of parameters (temperature and chemical potential) where the wet and non-wet phases coexist. Emphasis is made on the analogies and differences between equilibrium and nonequilibrium wetting.Comment: 5 pages, 3 figures, needs aipproc.cls; 7th Granada Seminar on Computational Physic

Nonequilibrium wetting transitions with short range forces

We analyze within mean-field theory as well as numerically a KPZ equation that describes nonequilibrium wetting. Both complete and critical wettitng transitions were found and characterized in detail. For one-dimensional substrates the critical wetting temperature is depressed by fluctuations. In addition, we have investigated a region in the space of parameters (temperature and chemical potential) where the wet and nonwet phases coexist. Finite-size scaling analysis of the interfacial detaching times indicates that the finite coexistence region survives in the thermodynamic limit. Within this region we have observed (stable or very long-lived) structures related to spatio-temporal intermittency in other systems. In the interfacial representation these structures exhibit perfect triangular (pyramidal) patterns in one (two dimensions), that are characterized by their slope and size distribution.Comment: 11 pages, 5 figures. To appear in Physical Review

Stochastic theory of non-equilibrium wetting

We study a Langevin equation describing non-equilibrium depinning and wetting transitions. Attention is focused on short-ranged attractive substrate-interface potentials. We confirm the existence of first order depinning transitions, in the temperature-chemical potential diagram, and a tricritical point beyond which the transition becomes a non-equilibrium complete wetting transition. The coexistence of pinned and depinned interfaces occurs over a finite area, in line with other non-equilibrium systems that exhibit first order transitions. In addition, we find two types of phase coexistence, one of which is characterized by spatio-temporal intermittency (STI). A finite size analysis of the depinning time is used to characterize the different coexisting regimes. Finally, a stationary distribution of characteristic triangles or facets was shown to be responsible for the structure of the STI phase.Comment: To appear in Europhys. Lett. // 3 figure

Movimentações dinâmico-complexas no espaço vocálico bilíngue (L1: português/L2: espanhol) : implicações atencionais e efeitos de tipo de tarefa de produção oral em atrito de L1

Através da presente pesquisa, discutimos o impacto da atenção (mais especificamente, atenção seletiva) e das demandas linguísticas e cognitivas de diferentes tipos de tarefas de produção oral, em relação aos padrões acústicos de altura/F1, anterioridade/posterioridade/F2 e duração (relativa) na produção vocálica tônica de aprendizes brasileiros de Espanhol (L2) residentes do sul do Rio Grande do Sul/Brasil, considerando o processo de atrito linguístico em L1. O estudo inicia, portanto, uma discussão sobre como os dados fonético-fonológicos refletem processos atencionais. Neste estudo, aplicamos uma metodologia conjugada entre análise de produto e análise de processo (LOWIE; VERSPOOR, 2019; YU; LOWIE, 2019), dada a complementariedade entre as mencionadas análises na exploração do desenvolvimento fonético-fonológico bilíngue. A pesquisa transversal (análise de produto) deste estudo foi realizada com 12 aprendizes adultas de Espanhol como L2 (Grupo Experimental) e 12 falantes monolíngues de PB (Grupo Controle). Em relação às tarefas, foi proposto que as participantes realizassem um teste atencional (d2 Test of Attention) e três tarefas linguísticas (com gravação de áudio), sendo elas: (i) Tarefa 'Nuvem de Palavras': Nesta tarefa, a partir da visualização de um filme silencioso curto, as participantes fizeram uma descrição oral sobre o vídeo assistido, utilizando 10-14 palavras listadas na tarefa; (ii) Tarefa de Leitura de Texto: Nesta tarefa linguística, as participantes leram um texto em voz alta de forma natural; e (iii) Tarefa de Leitura de Frase-Veículo: Esta tarefa correspondeu a uma atividade de leitura de enunciados. Por sua vez, na pesquisa longitudinal (análise de processo), acompanhamos uma aprendiz adulta de Espanhol como L2. O estudo longitudinal visou, portanto, à observação do desenvolvimento bilíngue, a partir da análise da variabilidade dos dados e de picos significativos que indicam mudança de estado/aprendizagem (VERSPOOR; DE BOT; LOWIE, 2011). A informante da etapa longitudinal participou de 16 sessões de coleta de dados em L1 e em L2, sendo uma coleta por semana, ao longo de um intervalo de quatro meses. Com base na literatura, assumimos tanto para as análises de produto como para as de processo que: (i) as bilíngues apresentariam produções vocálicas distintas entre L1 e L2, bem como produções de PB diferenciadas do grupo de monolíngues dessa língua (evidenciando-se, assim, atrito linguístico de L1); (ii) as tarefas de produção menos controladas poderiam demonstrar dados mais naturais nas produções bilíngues; (iii) no que diz respeito à capacidade atencional, bilíngues com altos índices de atenção mostrariam uma produção vocálica mais aproximada aos padrões nativos de cada um dos dois sistemas, mesmo em tarefas de produção mais livres. Dessa forma, altos índices atencionais levariam a uma maior "resistência" ao atrito linguístico. Com relação aos resultados, a partir dos dados do estudo transversal, observamos a ocorrência de um processo dinâmico de atrito de L1, principalmente, na vogal média baixa /ɛ/ e nas durações relativas de /e, i, u/. Além disso, os resultados apontam que há maior incidência de atrito de L1 nas tarefas de contexto linguístico menos controlado (Tarefa 'Leitura de Texto' e Tarefa 'Nuvem de Palavras'). No que diz respeito à capacidade atencional, prevíamos que altos índices atencionais levariam a uma maior "resistência" ao atrito linguístico. No entanto, o que observamos foi o oposto, pois quanto mais alto o índice atencional, mais diferenciada era a produção bilíngue em L1 das produções do Grupo Controle (monolíngues de PB). Essa diferença se deve a uma hiperarticulação das produções bilíngues em L1. Portanto, ao passo que a atenção ajudou a preservar as categorias de L1 frente à possibilidade de assimilação aos padrões de L2, essa preservação se deu através de um processo de atrito, não em direção ao padrão de L2, mas de uma dissimilação, ou hiperarticulação, dos padrões de L1. De forma semelhante, nos resultados do estudo longitudinal, também observamos um processo de dissimilação vocálica em L1 (em duração relativa nas vogais /a/ e /ɛ/; em anterioridade/posterioridade na vogal /e/; em altura na vogal /o/), influenciado, principalmente, pelo contato mais frequente com a L2. Consequentemente, esse processo impulsionou a manifestação de atrito de L1, pois ao mesmo tempo em que a L2 foi refinada, o subsistema de L1 também passou por um processo de auto organização. Sendo assim, o estudo longitudinal permitiu observar como ocorre, ao longo do tempo, o processo de atrito de L1 a partir de uma dissimilação vocálica. Com base nesses resultados, esperamos que o presente trabalho tenha prestado sua contribuição, especificamente à Psicolinguística e aos trabalhos em Desenvolvimento Fonético-Fonológico de L2, ao ressaltar a importância da construção de uma ponte entre os achados de atrito linguístico de L1 e construtos cognitivos, tal como 'atenção', no desenvolvimento fonético-fonológico bilíngue.In this study, we discuss the impact of attention (more specifically, selective attention) and the linguistic and cognitive demands of different types of oral production tasks, in relation to the acoustic patterns of vowel height/F1, frontness/backness/F2 and (relative) duration. We investigate the production of stressed vowels by Brazilian learners of Spanish (L2) living in the south of Rio Grande do Sul/Brazil, considering the process of L1 attrition. Therefore, the study initiates a discussion on how phonetic-phonological data reflect attentional processes. In this study, we apply a combined methodology between 'product' and 'process' analyses (LOWIE; VERSPOOR, 2019; YU; LOWIE, 2019), given the complementarity between the aforementioned approaches in exploring bilingual phonetic-phonological development. The cross-sectional component (product analysis) of this study was carried out with 12 adult learners of Spanish as L2 (Experimental Group) and 12 monolingual speakers of BP (Control Group). Regarding the tasks, the participants were askd to take an attention test (d2 Test of Attention) and three language tasks (audio recordings), namely: (i) 'Word Cloud' task: In this task, after watching a short silent film, participants made an oral description of the video, using 10-14 words listed in the task; (ii) Text Reading Task: In this language task, participants read a text aloud in a natural way; and (iii) Carrier Sentence Reading Task: This task consisted of a sentence reading activity. In turn, in the longitudinal study (process analysis), we investigated the language development process by an adult learner of L2 Spanish. The longitudinal study, therefore, aimed to map bilingual development based on the analysis of data variability and significant peaks, which indicate phase changes (VERSPOOR; DE BOT; LOWIE, 2011). The student in the longitudinal study took part in 16 data collection sessions in both languages, with one collection per week, over a period of four months. Based on the literature, for both product and process analyses, we assumed that: (i) bilinguals would present distinct vowel productions in each one of their languages, as well as different BP productions when compared to the monolingual group (which characterizes L1 attrition); (ii) less controlled production tasks should elicit more natural data in the bilingual productions; (iii) with regard to their attentional capacity, bilinguals exhibiting high levels of attention would show acoustic patterns that should more closely resemble the native standards of each of the two systems, even in less-controlled production tasks. Thus, high attentional rates would lead to a greater "resistance" to language attrition. With regard to the results, the cross-sectional study data showed the occurrence of a dynamic process of L1 attrition, mainly in the mid-low vowel /ɛ/ and in the relative durations of /e, i, u/. In addition, the results indicate that there was a higher rate of L1 attrition in less controlled tasks ('Text Reading' and 'Word Cloud' Tasks).With regard to the role played by attentional capacity, we had predicted that high attentional rates would lead to greater "resistance" to language attrition. However, we observed the opposite pattern, because the higher the attentional rates, the more different the bilinguals’ L1 productions were when compared to the Control Group data. This difference may be due to a hyperarticulation pattern found in the L1 produced by the bilingual participants. In other words, although attention helped to preserve L1 categories against L2 assimilation, this preservation took place through a process of attrition, manifested as a dissimilatory or hyperarticulated L1 pattern. With regard to the data obtained in the longitudinal study, we also observed a process of vowel dissimilation in the participant's L1 (relative duration in /a/ and /ɛ/; frontness/backness in /e/; height in /o/), mainly influenced by a more frequent contact with the L2. Consequently, this process boosted the manifestation of L1 attrition. Therefore, the longitudinal study also allowed us to observe how the L1 attrition process occurs through a process of vowel dissimilation. Based on these results, we assume that the present work has paved new research avenues to the fields of Psycholinguistics and L2 Phonetic-Phonological Development, by bridging the gap between L1 attrition data and cognitive constructs, such as 'attention', in bilingual phonetic-phonological development

Generic two-phase coexistence in nonequilibrium systems

Gibbs' phase rule states that two-phase coexistence of a single-component system, characterized by an n-dimensional parameter-space, may occur in an n-1-dimensional region. For example, the two equilibrium phases of the Ising model coexist on a line in the temperature-magnetic-field phase diagram. Nonequilibrium systems may violate this rule and several models, where phase coexistence occurs over a finite (n-dimensional) region of the parameter space, have been reported. The first example of this behaviour was found in Toom's model [Toom,Geoff,GG], that exhibits generic bistability, i.e. two-phase coexistence over a finite region of its two-dimensional parameter space (see Section 1). In addition to its interest as a genuine nonequilibrium property, generic multistability, defined as a generalization of bistability, is both of practical and theoretical relevance. In particular, it has been used recently to argue that some complex structures appearing in nature could be truly stable rather than metastable (with important applications in theoretical biology), and as the theoretical basis for an error-correction method in computer science (see [GG,Gacs] for an illuminating and pedagogical discussion of these ideas).Comment: 7 pages, 6 figures, to appear in Eur. Phys. J. B, svjour.cls and svepj.clo neede

A semantic-based approach to attain reproducibility of computational environments in scientific workflows: a case study

Reproducible research in scientific workflows is often addressed by tracking the provenance of the produced results. While this approach allows inspecting intermediate and final results, improves understanding, and permits replaying a workflow execution, it does not ensure that the computational environment is available for subsequent executions to reproduce the experiment. In this work, we propose describing the resources involved in the execution of an experiment using a set of semantic vocabularies, so as to conserve the computational environment. We define a process for documenting the workflow application, management system, and their dependencies based on 4 domain ontologies. We then conduct an experimental evaluation using a real workflow application on an academic and a public Cloud platform. Results show that our approach can reproduce an equivalent execution environment of a predefined virtual machine image on both computing platforms

Orientational order in Deposits of Magnetic Particles

We present preliminary results for the orientational order in deposits of dipolar particles, on one dimensional substrates. The deposits are generated using a model where the incoming dipolar particle interacts with the other particles in the deposit via a dipole-dipole potential. The interdipolar vectors are restricted to lie on a square lattice although the dipole moments are free to rotate in three dimensions. The path of the incoming particle is generated through a Monte Carlo scheme controlled by an effective temperature T, the case of pure diffusion-limited deposition corresponding to T=infinity$. We calculate the ferromagnetic and nematic order parameters and the dipolar orientational probability density of the deposits, at various stages of growth and two effective temperatures. The dipolar angular correlations along the rows and columns of the lattice are also investigated. We find that the orientational order of the deposits depends strongly on the lattice structure, the stage of growth and the effective temperature.Comment: 18 pages, 6 figure